1.7. Hygienic behaviour

Hygienic behaviour
is defined as the bees’ ability to detect and remove diseased brood from the
nest (Rothenbuhler, 1964). Hygienic behaviour was first described in the 1930s
when researchers sought to determine the mechanism by which some honey bee
colonies were resistant to American foulbrood (reviewed in Spivak and Gilliam,
1993). In the 1980s, it was shown that hygienic behaviour was also the primary
mechanism of resistance to chalkbrood (Gilliam et al., 1983), although resistance to this disease involves other
factors as well, such as differences in the susceptibility of different
colonies or even between patrilines within colonies (Invernizzi et al., 2009; Jensen et al., 2009b).

Hygienic behaviour assays, involving
killing brood by freezing or by piercing pupae with a pin (methods described in
the BEEBOOK paper on queen rearing
and selection (Büchler et al., 2013)
are indirect, and record the proportion of dead brood removed by a colony after
a particular amount of time. Most, but not all colonies, show a good
correlation between removal of freeze-killed brood and resistance to
chalkbrood. However, researchers and beekeepers cannot assume that the ability
of a colony to remove dead brood within a certain time will ensure colony-level
resistance to chalkbrood. It is very important, especially for breeding
purposes, to directly challenge colonies with A. apis in addition to the
freeze-kill or pin-kill brood assay (See paragraph 1.5.1. Infection bioassay of
colonies) and subsequent observation of the bees’ response to the challenged
brood (Palacio et al., 2010).